The present invention relates to a puffer-type gas blast switch as defined in the preamble of claim 1.
Puffer-type gas blast switches with insulating nozzles have relatively long arc periods because at the time the contact is severed there is present a comparatively low gas pressure which is not yet sufficient to quench strong arc currents. A sufficiently high pressure builds up only after the switch has passed through a larger stroke. In such switches there essentially exist the following drawbacks: the arc is drawn out, it burns a long time, and quenching gas is wasted at a time when there is as yet no chance of quenching. The energy consumption in the switching path becomes high as a result of these influences and either limits the circuit breaking capability of such switches or necessitates comparatively large quenching chambers so as to avoid undue pressure increases.
Puffer-type switches are known in which the contact piece which is actuated by the switch drive as well as the counter contact piece are movable. In such switches the counter contact piece is controlled by the movement of a piston. However, such switches are costly and complicated and can therefore not be used in an atmosphere containing SF.sub.6 dissociation products, as disclosed in German Offenlegungsschrift No. 2,100,808.
German Offenlegungsschrift No. 2,708,546, and corresponding U.S. application Ser. No. 881,719, filed Feb. 27th, 1978, now U.S, Pat. No. 4,211,904, issued July 8th, 1980, also discloses a puffer-type gas blast circuit breaker in which a switching contact disposed in an insulating nozzle is mounted to be axially displaceable in a guide actuated by a pull rod. In the on-state, the switching contact disposed in the insulating nozzle is latched in a stationary counter contact. For breaking the circuit, the guide, the insulating nozzle and cylinder connected with these parts are moved in the OFF direction. Due to the latching, the contact disposed in the insulating sleeve is pulled out of the guide whereby an annular projection of the switching contact abuts against the upper edge of the guide. At this moment, the switching contacts are pulled apart and the contact that has been pulled out of the guide is accelerated by the compression spring to spring back into the guide, or the insulating nozzle, respectively.
Although with such a gas blast switch the arc period can be shortened and blasting of the arc before reaching the quenching distance can be prevented, a correspondingly large stroke is required to attain a sufficiently high pressure in the cylinder, causing the contact to be pulled out by a corresponding amount. This makes it impossible to maintain the optimum quenching distance.